If you smuggle goods into the country, they may be ...... by the customs authority.

If you smuggle goods into the country, they may be confiscated by the customs authority.
In this context, "confiscated" means seized or taken away by authority due to illegal smuggling activities. When goods are confiscated, they are forcibly taken away from the smuggler by the customs authority as a penalty for violating customs laws. Therefore, "confiscated" is the most suitable term to complete the sentence.